The conservation commission is hereby given power to establish state wild life sanctuaries and may by appropriate resolution accept as such, privately owned lands, when the owners or lessees thereof shall file with said commission an application dedicating such lands for such purposes. The commission may accept such dedication only after it shall have determined that the application is made in good faith, that the said lands are suitable for the declared purposes, that the dedication and operation of the proposed wild life sanctuary will tend to increase the supply of desirable wild life in that vicinity and will otherwise be in the public interest. Applications shall not be approved for areas of less than 20 acres nor for more than 1,500 acres or for periods of less than 5 years.